Human Biology Exam 2 Study Guide: Muscular, Respiratory, Digestive Systems & Genetics

Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system enables movement, posture, and heat production. Muscle contraction is based on the sliding filament mechanism within muscle cells (muscle fibers).

• Sarcomere: The basic contractile unit of muscle, composed of repeating segments of actin (thin) and myosin (thick) filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin filaments and pull them inward, shortening the sarcomere.

• Actin and Myosin: Actin forms the thin filaments, while myosin forms the thick filaments with protruding heads that interact with actin.

• Function of the Sarcomere: Generates force and shortens during contraction, leading to muscle movement.

Example: During biceps contraction, sarcomeres in the muscle fibers shorten, pulling the forearm upward.

Electrical Impulses and Muscle Contraction

Muscle contraction is initiated by electrical signals (action potentials) from motor neurons.

• Action Potential: A rapid change in membrane potential that travels along the neuron and muscle fiber, triggering contraction.

• Neuromuscular Junction: The synapse where a motor neuron communicates with a muscle fiber, releasing neurotransmitters (e.g., acetylcholine) to initiate contraction.

• Order of Events:

  1. Action potential arrives at the neuromuscular junction.

  2. Acetylcholine is released, binding to receptors on the muscle cell membrane.

  3. Muscle cell membrane depolarizes, generating an action potential.

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Myosin heads bind to actin, initiating contraction.

Isotonic vs. Isometric Contractions:

• Isotonic: Muscle changes length (shortens or lengthens) while tension remains constant (e.g., lifting a weight).

• Isometric: Muscle length remains the same while tension increases (e.g., holding a weight steady).

Muscle Groups and Body Heat

• Major Muscle Groups: Include biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and more.

• Heat Generation: Most body heat is generated by muscle activity, especially during shivering or exercise.

• Muscles and Body Cavities: Diaphragm separates the thoracic and abdominal cavities; intercostal muscles assist in breathing.

Human Respiratory System

Significance and Structure

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide, essential for cellular respiration.

• Upper Respiratory Tract: Includes nose, nasal cavity, pharynx, and larynx. Functions: filtering, warming, and humidifying air.

• Lower Respiratory Tract: Includes trachea, bronchi, bronchioles, and lungs. Functions: conducting air to alveoli for gas exchange.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, drawing air in.

• Exhalation (Expiration): Muscles relax, thoracic volume decreases, lung pressure increases, pushing air out.

• Pressure Changes: Air flows from high to low pressure; during inhalation, lung pressure drops below atmospheric pressure.

• Intercostal Muscles: Assist in expanding and contracting the rib cage during breathing.

Equation for Pressure-Volume Relationship (Boyle's Law):

$P_1 V_1 = P_2 V_2$

Blood Flow and Gas Exchange

• Oxygen-Rich Blood: Returns from the lungs to the left atrium, then left ventricle, and is pumped to the body.

• Order of Blood Flow: Right atrium → right ventricle → lungs → left atrium → left ventricle → body.

Respiratory Diseases and Disorders

• Include asthma, bronchitis, emphysema, pneumonia, and lung cancer.

• Disorders can impair gas exchange and oxygen delivery.

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

• Main Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Function of Enzymes: Biological catalysts that speed up the breakdown of food; produced in the mouth, stomach, pancreas, and small intestine.

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for nutrient absorption.

Digestion and Metabolism

• Peristalsis: Wave-like muscle contractions that move food through the digestive tract.

• Standard Metabolic Rate (SMR): The rate of energy expenditure under specific conditions (e.g., at rest, fasting).

• Basal Metabolic Rate (BMR): The minimum energy required to maintain basic physiological functions at rest.

• "My Plate": A guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Human Genetics and Inheritance

Genes, Chromosomes, and Inheritance

Genetics is the scientific study of heredity and variation in organisms.

• Gene: A segment of DNA that codes for a specific protein or trait.

• Chromosome: A structure composed of DNA and proteins, carrying genetic information; humans have 23 pairs.

• Genome: The complete set of genes or genetic material in an organism.

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

• Karyotype: An organized profile of an individual's chromosomes, used to detect chromosomal abnormalities.

Genotype, Phenotype, and Patterns of Inheritance

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits or characteristics (e.g., brown eyes).

• Punnett Square: A diagram used to predict the outcome of genetic crosses.

• Dominant Allele: Expressed when present (e.g., A).

• Recessive Allele: Expressed only when two copies are present (e.g., a).

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Mendelian Laws and Non-Mendelian Inheritance

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white = pink flowers).

• Codominance: Both alleles are fully expressed (e.g., AB blood type).

• Polygenic Inheritance: Multiple genes influence a single trait (e.g., skin color).

• Environmental Impact: Environment can affect gene expression (e.g., nutrition influencing height).

• Linked Genes: Genes located close together on the same chromosome tend to be inherited together.

• Sex-Linked Genes: Genes located on sex chromosomes (X or Y), often showing different inheritance patterns in males and females.

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Term	Definition	Example
Genotype	Genetic makeup (allele combination)	AA, Aa, aa
Phenotype	Observable trait	Tall, short
Homozygous	Two identical alleles	AA or aa
Heterozygous	Two different alleles	Aa
Dominant	Expressed allele	A
Recessive	Masked by dominant	a

Example: A cross between two heterozygous parents (Aa x Aa) yields a 3:1 ratio of dominant to recessive phenotypes.

Additional info: Some dominant disorders are lethal because a single copy of the mutant allele disrupts essential functions, while recessive disorders persist because carriers (heterozygotes) are unaffected and can pass the allele to offspring.